A variety of wireless communication services using a wireless network are provided as computer, electronic and communication technology develops by leaps and bounds. A most basic wireless communication service, which is a wireless voice communication service providing voice communication for subscribers of mobile communication terminal by wireless scheme, has a characteristic to provide service regardless of time and place. Further, besides supplementing a voice communication service by providing a message service, a wireless internet service is brought up recently which provides an Internet communication service for subscribers of mobile communication terminal through a wireless communication network.
Herein, services which are provided by Code Division Multiple Access (hereinafter, referred to “CDMA”) mobile communication system have been developed not only to a voice service but also to multimedia communication services which transmit and receive data such as circuit data, packet data and etc.
Further, recently, an International Mobile Telecommunication 2000 (hereinafter, referred to as IMT-2000), which is the 3G mobile communication system, has been commercialized by the development of information and communication. The IMT-2000 is the service which is a CDMA 2000 1x, 3x, EV-DO, WCDMA (Wideband CDMA) and etc., and can provide a wireless internet at transmission rate, more than 144 Kbps much faster than 14.4 Kbps or 56 Kbps, data transmission rate supported in IS-95A and IS-95B network, by using IS-95C network developed from an existing IS-95A and IS-95B network. In Particular, if using IMT-2000 service, it is possible to provide various multimedia services (for example AOD, VOD and etc.) at much faster rate as well as the improvement of existing voice and WAP services quality.
However, due to high cost for constructing a base station, the charge for using is high in an existing mobile communication system. Further, due to a small screen size of a mobile communication terminal, there is a limit to provide very high speed wireless internet services for example a limit to use contents. Furthermore, there is a limit to provide public services owing to the problem of radio wave interference and narrow using coverage in Wireless Local Area Network (hereinafter, referred to as WLAN). Therefore, in order to guarantee portability and mobility, and provide very high speed wireless internet services at a lower charge, mobile internet technology is emerged which uses a TDD scheme for a duplex scheme and uses a OFDM scheme for a modulation scheme.
Herein, the TDD scheme is a two-way transmission scheme which allocates uplink and downlink in turns timely at the same frequency band. The TDD scheme has higher efficiency than a Frequency Division Duplex (hereinafter, referred to as FDD) scheme allocating two different frequency to uplink and downlink, and has a characteristic to be suitable for transmitting asymmetric or bursting applications.
Herein, an OFDM scheme is a next generation communication scheme adopted as a standard of a wireless LAN (802.11g,a), a W-MAN (802.16), a digital broadcasting, a VDSL and etc., and is a digital modulation scheme for improving transmission speed per band width and preventing multipath interference. The biggest characteristic of the OFDM scheme is to have a orthogonality between sub-carriers. That is, it is possible to have an excellent characteristic in multipath fading and to improve transmission content largely by adjusting data transmission rate corresponding to each sub-carrier in the ration of signal to noise in a particular sub-carrier. Furthermore, the OFDM scheme has a strong characteristic in narrow-band interference because it has influence only on some sub-carriers.
However, the OFDM scheme has a characteristic to be sensitive to frequency offset of a carrier and phase noise, which becomes a main cause to affect the security of orthogonality, that is, to deteriorate the capacity of a system, to have relatively a high ratio of average power to the maximum power comparative to one of a single carrier modulation, and to decrease power efficiency of an RF power amplifier. It is possible to overcome the interference between symbols due to multipath channel while it is impossible to reconstruct the signal transmitted to the sub-channel when the attenuation of a particular sub-channel is serious. In order to prevent this, it is possible to solve the problem using error correction code which is called a Coded OFDM (hereinafter, referred to as “COFDM”). Herein, it is possible to use both block code such as Reed-Solomon code and convolutional code as the error correction codes and to take an advantage of a connection code coupling the two codes, turbo codes and etc., too.
There is a High-speed Portable internet (hereinafter, referred to as “HPi”) system as representative portable internet technology. The HPi system is the next generation wireless internet technology which the Telecommunications Technology Association (hereinafter, referred to as “TTA”) is developing in association with Samsung Electronics Co., Ltd. and the Electronics and Telecommunications Research Institute (hereinafter, referred to as “ETRI”).
The HPi system uses the frequency band of 2.3 GHz and, as described above, uses the TDD as a duplex scheme and the OFDM as a modulation scheme. Furthermore, the HPi system provides the mobility of 60 Km/h and is a wireless data system which has uplink and downlink asymmetric transmission characteristic considering a downlink transmission speed is 24.8 Mbps but a uplink transmission speed is 5.2 Mbps.
FIG. 1 is a diagram schematically showing an HPi system.
As shown in FIG. 1, the HPi system may include an Access Terminal 100 (hereinafter, referred to as “AT”), an Access Point 110 (hereinafter, referred to as “AP”), a Packet Access Router 120 (hereinafter, referred to as “PAR”), a Packet Data Serving Node 130 (hereinafter, referred to as “PDSN”), a Packet Data Gateway Node 140 (hereinafter, referred to as “PDGN”), an Authentication Authorization Accounting 150 (hereinafter, referred to as “AAA”), an IP network 160 and an internet 170.
Herein, the AT 100 refers to a mobile communication terminal which uses a very high speed wireless internet service by connecting with the HPi system and has low power Radio Frequency (hereinafter, referred to as “RF”)/Intermediate Frequency (hereinafter, referred to as “IF”) module and controller function, a Media Access Control (hereinafter, referred to as “MAC”) frame variable control function depending on service characteristics and radio wave circumstance, a handover function, authentication and encryption functions and etc.
The AP 110 transmits the data received from PAR 120 as a base station of the HPi system, and has a low-power RF/IF module and controller function, OFDMA/TDD packet scheduling and channel multiplex function, an MAC frame variable control function depending on service characteristics and radio wave circumstances, a 50 Mbps high speed traffic real-time control function, a handover function, and etc.
Further, the AT 100 and the AP 110 have a 50 Mbps packet transmission modulating demodulating function for data transmission, a high packet channel coding function, a real-time modem control function, and etc.
The PAR 120 is a packet access router which accommodates a number of the AP 110, has a handover control function of AP 100, a handover control function of the PAR 120, a packet routing function, an internet connection function and etc., and further connects with IP network.
The PDSN 130 relay transmitting and receiving of packet data between an external packet data service server such as the internet 170, etc. and a base station through the IP network 160 and administers the location information data of a mobile communication terminal including the AT 100.
The PDGN 140 performs a routing which traces and then connects with an external packet data service server of the internet 170, etc. Further, the AAA 150 links the PDSN 130, carries out accounting for a packet data used by the AT 100 and authenticates the connection with the AP 100.
The IP network 160 connects with the PDSN 130, PDGN 140 and the AAA 150, and then transmits a packet data received from an external packet data service server such as the internet 170, etc. to the AP 100.
Meanwhile, in a mobile communication system, a mobile communication service region has been generally divided into a plurality of cells using a frequency reuse concept in order to extend the coverage of a mobile communication network and a Base Station (hereinafter, referred to as “BS”) have been installed around the center of each of the cells in order to handle the mobile communication service. Herein, the ratio of a cell is set depending on the strength of a signal or the amount of data traffic. That is, the ratio of a cell is set small in an urban center in which there is much amount of traffic and the ratio of a cell is set large in a suburb in which there is comparatively less amount of data traffic so that the amount of traffic should not exceed the treatment content of the wireless BS handling a corresponding mobile communication service.
There have been shade regions of radio waves such as a basement, a building's interior, a tunnel, etc. which it is difficult for the radio wave to reach in spite of these effort to support better mobile communication services controlling the ratio of a cell depending on the frequency reuse concept or the amount of traffic, etc. It may cause undesirable results in cell-construction as well as in weakening the economical efficiency due to equipping expenses, installing expenses and maintenance and repair expenses, etc. to equip a plurality of new base stations for solving the shade of radio wave in the shade regions of radio wave.
In order to solve the above-mentioned problem, it is possible to provide mobile communication services using an optical repeater system in these shade regions of radio waves. The optical repeater system can solve the problem of the shade of radio wave by allowing a communication channel allocated to a base station to transmit to the shade region of radio waves through an optical transmission scheme using the optical transmission scheme. Particularly, it is preferable to use an optical repeater having a small cell ratio because a radio waves loss is more, a diffraction effect is small, and building transmission loss is large in 2.5G, PCS, and 3G using a higher frequency than a 2G mobile communication system.
Meanwhile, in order to repeat a wireless signal between a base station and a terminal, the optical repeater might be capable of distinguishing an uplink signal from a downlink signal. The optical repeater of a mobile communication system must distinguish an uplink signal from a downlink signal by using a duplex when using the FDD scheme. However, it is impossible to distinguish an uplink signal from a downlink signal by using a duplex because it uses the same frequency in order to distinguish an uplink signal from a downlink signal when using the TDD scheme like the HPi system, etc. Accordingly, the optical repeater using the TDD scheme is able to distinguish an uplink signal from a downlink signal by using a switch and provide a path for each signal selectively. In order to do this, it is necessary for the controlling signal to distinguish between the starting point of a downlink signal and the one of an uplink signal exactly and to change a shifting path by controlling the path of a switch depending on each of signals. In addition, the optical repeater can receive the controlling signal described above.
However, because manufacturers of base stations and optical repeaters are generally various, in order to receive a switch controlling signal transmitted from a base station, it causes problems that an extra fee is needed for installing another modem in an optical repeater and the cause of obstacle is not founded easily for controlling a switch of an optical repeater. Further, it is a defect that an extra procedure compensating the controlling signal by delay value of an optical cable is needed and an extra fee corresponding to this is needed.
Therefore, the plan is demanded which can distinguish between a downlink signal and an uplink signal in the optical repeater itself and generate a switching timing signal to provide a path of each signal selectively in order to use the optical repeater even in the mobile communication system of the TDD scheme.